In a major pre-poll incident in West Bengal, unknown gunmen shot dead Trinamool Congress vice-president Sachin Mukherjee while he was returning home in Garia in South 24 Parganas district on Sunday night.

The incident, dubbed by the Trinamool Congress as 'handiwork of CPI-M', sparked off tension in the entire area, prompting Trinamool chief Mamata Banerjee to rush to the spot with followers, demanding immediate arrest of the assailants.

The state IGP (Law and Order) Rajkanojia told PTI that Mukherjee was shot at a point blank range and died on the spot. Police launched a manhunt to nab the assailants.

According to Sophandeb Chattopadhyay, Trinamool Congress chief whip in state assembly, Mukherjee was a trade union leader and was known as a good organiser in the party.

Accusing the CPI-M of having a hand in the crime, Chattopadhyay said that Mukherjee joined the Trinamool Congress from Congress during the formation of the new party.

Quoting Mamata Banerjee, who was leading a procession in the area, Chattopadhyay said a conspiracy had been hatched to annihilate Opposition leaders before the election.

"If a leader of a political party is killed in this manner, what is the security of a commonman in the state", Chattopadhyay said, quoting Banerjee.